Control Strategy And Research Between Grid Connected And Island Operation Modes Of Microgrid

With the rapid development of smart grid, more and more countries in the world pay attention to microgrid because the advantages of its low loss, high utilization rate, improving electric energy quality. Coordinated control of the distributed generation, smooth transition between grid-connected and islanding operation mode, these are the key technical problems of microgrid.Microgrid can make full use of clean energy and the reliable operation based on photovoltaic and battery, according to the characteristics of the distributed generation, control strategies are easily proposed to achieve smooth transition in this thesis Microgrid use the master-slave control structure, photovoltaic cells use PQ control strategy and the battery adopts V/f control strategy in the islanding operation. The battery output power can be controlled in a certain range, and the battery can provide the voltage and frequency reference for photovoltaic. In grid-connected operation, battery and photovoltaic cells use PQ control strategy. Photovoltaic array to generate electric energy is big, for part load, a part of charging the battery, but also to power transmission. When power generation is not enough, the battery regulate the grid connected power and guarantee power supply of the important load. This thesis uses a phase-locked loop, phase locking synchronous of island mode, pre-synchronizing and the improved of the main controller, reduces the effect of the switching time, thus realizes the smooth transition of microgrid.The software MATLAB/Simulink is utilized to build the verifiable of microgrid, including photovoltaic cells, the battery unit, PQ control, V/f control, islanding detection module. Simulations in grid-connected operation, islanding and smooth transition of two modes, show that control strategies can satisfy power balance, smooth transition and power supply of the important load. To build an experimental platform of microgrid based on completing the simulation, and design two inverters, power ratings are 8kW. First the inverter start the experiment of on-grid and off-grid, and then start the switch experiment of microgrid, the voltage switching waveform confirm that control strategies is effective. Microgrid prototype is good, can realize reliable operation and smooth switch.